text: The melanocortins are a family of neuropeptide hormones which are the ligands of the melanocortin receptors. The melanocortin system consists of melanocortin receptors, ligands, and accessory proteins. The genes of the melanocortin system are found in chordates. Melanocortins were originally named so because their earliest known function was in melanogenesis. It is now known that the melanocortin system regulates diverse functions throughout the body, including inflammatory response, fibrosis, melanogenesis, steroidogenesis, energy homeostasis, sexual function, and exocrine gland function. 
  There are four endogenous melanocortin agonists which are derived from post-transcriptional processing of the precursor molecule proopiomelanocortin (POMC) (Figure 1). They are Adrenocorticotropic hormone (ACTH), a-melanocyte stimulating hormone (MSH), b-MSH, and g-MSH. In addition to agonists which activate melanocortin receptors , there are two antagonists which inhibit receptor activity, Agouti and Agouti-related protein (Agrp). Lastly, the ligand β-defensin 3 acts as a neutral melanocortin receptor antagonist.